It is known to form polyketones by the polymerization of carbon monoxide and one or more olefins by a vapor phase polymerization process. For example, U.S. Pat. No. 4,778,876 of M. J. Doyle et al. describes such a process in which the monomers are contacted with the catalyst compositions in the substantial absence of a liquid, non-polymerizable diluent. Any small quantity of diluent that might be present is vaporized and present in exclusively the gaseous state (Col. 1, lines 35-40).